Nanog expression is negatively regulated by protein kinase C activities in human cancer cell lines

Abstract

Nanog is a transcription factor that is essential for the maintenance of pluripotency of the embryonic stem cells. Nanog has been shown to be expressed in various kinds of human tumors, suggesting a role in tumorigenesis. In this study, we found that Nanog expression was upregulated by inhibition of protein kinase C (PKC) activity in six human cancer cell lines examined. In a Nanog non-expressing human nasopharyngeal carcinoma cell line, NPC-076, Nanog mRNA level and protein level were both induced and dose-dependently promoted by exposure to PKC inhibitors. Knockdown experiments showed that PKCα and PKCδ were two subtypes exerted most of the effect. The reporter assay showed that Nanog promoter activity was promoted by exposure of the cells to PKC inhibitors and the effect was dependent on the presence of the Octamer-Sox composite element. The involvement of Octamer-Sox composite element was further supported by the observation that silencing of Oct4 and Sox2 in NPC-076 cells attenuated the effects of PKC inhibitors. In Nanog-expressing human embryonal carcinoma cell lines, NT2/D1 and NCCIT, Nanog expression was suppressed by exposure to PKC activator Phorbol-12-myristate-13-acetate (PMA). Further study showed that overexpression of PKCα elicited a repressive effect on Nanog expression in NT2/D1 cells. Consistently, mutation of the Octamer-Sox composite element abolished the suppressive effect by PKC activator. Nanog expression was of cellular significance in that ectopic expression in NPC-076 stimulated cell proliferation and knockdown of the endogenous Nanog expression in NT2/D1-suppressed cell proliferation.

Regulation of NANOG in cancer cells

“…The induction of NANOG expression by PKC inhibitors required Octamer–Sox composite element. The reasons behind the discrepancy of the differential PKC effects on NANOG expression in the two studies need further investigation. Another study reported that NANOG not only promoted the activity and expression of focal adhesion kinase (FAK) by binding the promoter region of FAK , but also interacted with FAK protein, which, in turn, phosphorylated NANOG at Tyr 35 and Tyr174 in a dose dependent manner .…”

“…Their results illustrate that phosphorylation of NANOG at certain sites is required for sustaining NANOG stability, dimerization, and regulating BMI1 and thus promoting tumorigenic properties in HNSCC cells . Unexpectedly, another group presented opposite results and conclusions for effects of PKC on NANOG . The authors investigated the relationship between PKC activity and NANOG expression in several human cancer cell lines including nasopharyngeal carcinoma NPC‐076, hepatocellular carcinoma (HepG2 and Hep3B), bladder carcinoma (HT1376 and T24), colorectal cancer (SW620), and embryonal carcinoma cells (NT2/D1 and NCCIT).…”

“…The authors investigated the relationship between PKC activity and NANOG expression in several human cancer cell lines including nasopharyngeal carcinoma NPC‐076, hepatocellular carcinoma (HepG2 and Hep3B), bladder carcinoma (HT1376 and T24), colorectal cancer (SW620), and embryonal carcinoma cells (NT2/D1 and NCCIT). They observed that either inhibition or knockdown PKC, particularly PKCα and PKCδ, dramatically promoted NANOG expression, and PKC inhibitors enhanced NANOG promoter activity, whereas activation of PKC by phorbol‐12‐myristate‐13‐acetate (PMA) suppressed NANOG and its target genes expression . The induction of NANOG expression by PKC inhibitors required Octamer–Sox composite element.…”

Protein Kinase C (PKC) Isozymes and Cancer

“…The activated Nanog induces antiapoptotic and proliferative factors, such as P-gp and the inhibitor of the apoptosis protein (IAP) family (e.g., cIAP-1, cIAP-2, and XIAP), and reduces cancer suppressor proteins, such as PDCD4, resulting in enhanced antiapoptosis and anticancer drug resistance [516][517][518]. On the other hand, a recent study has suggested that Nanog expression is also upregulated by inhibition of PKC activity, especially PKC and activity, in human cancer cell lines [519].…”

Protein Kinases and Associated Pathways in Pluripotent State and Lineage Differentiation

“…Protein kinase C (PKC) seems to be a requirement for the differentiation of hESCs [99, 100]. Its inhibition maintains mouse, rat and human pluripotency by upregulating Nanog expression in the presence of the Oct-Sox composite element [101] without the need of STAT3 activation or Erk/Gsk3 signaling pathway inhibition [102, 103]. …”